Subject: [PATCH V1 3/5] mtd: m25p80: add the quad-read support

From: [email-masked] (Huang Shijie)
Date: Fri, 23 Aug 2013 17:25:21 +0800

? 2013?08?23? 17:05, yuhang wang ??:
>> +       u16 sr_cr;
>> >  +       int ret;
>> >
>> >    #ifdef CONFIG_MTD_OF_PARTS
>> >           if (!of_device_is_available(np))
>> >  @@ -1014,6 +1050,21 @@ static int m25p_probe(struct spi_device *spi)
>> >           else
>> >                   flash->read_opcode = OPCODE_NORM_READ;
>> >
>> >  +       /* Try to enable the Quad Read */
>> >  +       if (np&&  of_property_read_bool(np, "m25p,quad-read")) {
>> >  +               /* The configuration register is set by the second byte. */
>> >  +               sr_cr = CR_QUAD<<  8;
>> >  +
>> >  +               /* Write the QUAD bit to the Configuration Register. */
>> >  +               write_enable(flash);
>> >  +               if (write_sr_cr(flash, sr_cr) == 0) {
>> >  +                       /* read back and check it */
>> >  +                       ret = read_cr(flash);
>> >  +                       if (ret>  0&&  (ret&  CR_QUAD))
>> >  +                               flash->read_opcode = OPCODE_QIOR;
>> >  +               }
>> >  +       }
>> >  +
> Well, M25p80.c support lots of flash devices, so driver should be as
> general as possible. Firstly not all the devices m25p80 supports set
> quad mode as your sequence, perhaps write_sr_cr can not match all the
It does not matter the NOR flash supports the write_sr_cr() or not,
If the NOR flash does not support the write_sr_cr(), it may fails, and 
you will not set the OPCODE_QIOR for the
m25p80_read.

> m25p80 flash. Secondly, why you only support QIOR(high performance)
> not QOR or DOR. Maybe QIOR seems too special, so what if user want to
> use QOR if he set quad mode in DTS.
>
Frankly speaking, i am reluctant to support the QIOR, it is a little 
slow. :)

So the the QIOR is lowest speed for QUADSPI controller, and i do not 
want to support the DOR.

In my new version, i add the support for DDR QIOR read which is the 
double rate of the QIOR.

The user should knows if the NOR flash supports the quad-read or not, 
and set the proper DT.

> Another point, if command changed to OPCODE_QIOR, there should also
> should be some correct in m25p_read. such as the number of dummy data.
I only need to change the read opcode.
> QIOR can support read without read command if set the certain bit in
> transfer, these aspects did not reflect in your patch.
>
For the Quadspi, it will handle the dummy by the LUT sequence, such as 
DDR QUAD read, the LUT sequence will
set proper dummy (6 cycles for S25FL128S). I do not need the m25p_read 
to set the dummy.

thanks
Huang Shijie